Antibacterial activity againstRalstonia solanacearumof the lipopeptides secreted from theBacillus amyloliquefaciensstrainFJAT‐2349

Abstract

Aims The aims of this study were to identify the structure of antibacterial lipopeptide (LP) produced by Bacillus amyloliquefaciens strain FJAT‐2349, to analyse the effects of the culture medium and temperature on LP production and to assess the biocontrol efficiency of the LPs against tomato bacterial wilt. Methods and Results Lipopeptides were extracted by acid precipitation and resolved in methanol and their structure was identified through LC‐QTOF‐MS/MS method. The antibacterial activities of the LPs were evaluated through inhibition zone experiments. The biocontrol efficiency of the LPs against tomato bacterial wilt was examined by a pot test. The LPs were composed of iturin (C14–C17 iturin A), fengycin (C14/C16 fengycin A, C14 fengycin B2, C16 fengycin A2/B2, C16–C17 fengycin B, C15 fengycin A derivatives and C15 fengycin B derivatives) and surfactin (C12–C16 surfactin A). Moreover, the composition of the LPs was significantly influenced by the culture medium and temperature; the contents of iturin, fengycin and surfactin varied within the range from 0·41–5·89, 4·54–181·67 and 2·05–19·65 mg l−1 in the different culture media and from 0·39–11·04, 1·45–215·14 and 7·79–24·43 mg l−1 under different culture temperatures respectively. The results indicated that the contents of the LP mixture, fengycin and surfactin secreted from FJAT‐2349 all decreased along with an increasing culture temperature. The fermentation supernatants and LP extracts had the strongest inhibition activities of Ralstonia solanacearum when strain FJAT‐2349 was incubated at 25°C using potato dextrose broth as the culture medium among all the assayed culture conditions. The purified fengycin was found to be the active antibacterial compound against R. solanacearum, but the purified surfactin was not. The pot experiments demonstrated that the LPs secreted from the strain FJAT‐2349 could effectively control the tomato bacterial wilt with a biocontrol efficiency of 97·6%. Conclusions The LPs secreted from strain FJAT‐2349 could serve as potential biocontrol agents against tomato bacterial wilt. Significance and Impact of the Study The LPs exhibited good potential applications in the biocontrol of tomato bacterial wilt.

Isolation, Identification and Characterization of Rhizobacteria Strains for Biological Control of Bacterial Wilt (Ralstonia solanacearum) of Eggplant in China

“…Similarly, in the operational group B. amyloliquefaciens, our results demonstrated that antibacterial activity was related to iturin and fengycin, as has been reported [46,47]. Strains IMA2, IMA6, IMA8 and IMA10 were able to produce iturin or both iturin and fengycin, corresponding to a higher antibacterial activity compared with IMA1 and IMA9 without lipopeptide production and with low antibacterial activity.…”

“…Similarly, there is no significant difference between the IMA2 and IMA8 in vivo assays, showing that iturin is the most important active ingredient. This is probably due to too little fengycin being secreted by IMA 8 under the same conditions, although few studies display that iturin and fengycin produced by B. amyloliquefaciens have high activity against R. solanacearum [46,47], and purified fengycin has stronger antibacterial activity than iturin [47]. By comparison, no lipopeptides are found in strains IMA 4, IMA 7 and IMA 11 except IMA4 but they also show higher disease control efficacy, possibly being associated with mechanisms of induced resistance [33,48].…”

Biocontrol of tomato bacterial wilt by the new strain Bacillus velezensis FJAT-46737 and its lipopeptides

“…The supernatant was adjusted to pH 2.0 with 3 mol/L HCl to obtain the crude lipopeptides. The extracted lipopeptides were dissolved in phosphate buffer and then lyophilized [32]. The obtained lipopeptide powder was dissolved in pure methanol for antimicrobial activity tests, for the qualitative and quantitative analyses and it was dissolved in water for the further pot experiments.…”

“…Qualitative and quantitative analyses of the lipopeptides were performed using liquid chromatography quadrupole time-of-flight tandem mass spectrometry (LC-QTOF-MS/MS) technology based on previous methods [32]. The structure of the lipopeptides was estimated by their accurate mass and MS/MS fragmentation patterns according to the literatures [33][34][35][36][37].…”

“…The culture media of A, B, C, D, E and F in Table S1 and temperatures of 20, 25, 30, 35 and 40 °C were selected for cultivating strain FJAT-46737. The antagonistic activities of the lipopeptides produced under different culture conditions were determined by the aforementioned agar disk diffusion method [32].…”